1. Field of the Invention
The present invention is generally directed to a spring structure for upholstered cushion seating, and is specifically directed to spring structure including a sinuous spring and a coil spring which is placed between a rigid support frame and the upholstery padding material in a sofa, chair or the like.
2. Description of Prior Art
Perhaps the most significant breakthrough in the development of modern seat cushions was the adaptation of a spring structure for upholstered cushion seating. Prior to the use of springs, cushions were simply stuffed with matting, fill or other soft fibers. After a period of use, the cushion stuffing would settle, often resulting in a hard, lumpy, uncomfortable cushion.
The advent of the coil spring solved many of the prior problems. The early coil springs were placed in a frame under the seat cushion padding in a sufficient number of rows to provide proper seating support. The coil springs advantageously provided a consistent spring resilience throughout the seating area. However, this manner of providing cushion seating was expensive due to the large number of coil springs needed to support a cushion in a consistent manner.
The development of the sinuous spring caused many manufacturers to adopt this spring as an economical substitute for the prohibitively priced coil spring structure. The sinuous springs have a zig-zag pattern and are disposed in an upwardly bending arc between two parallel sides of a frame. Rows of sinuous wire springs are generally attached in a parallel alignment between the front and rear walls of cushion seating frames, offering both comfort and resilience. While the substitution of sinuous springs for coil springs reduced the amount of wire and the cost of the springs by between 60 and 80%, the firmness and comfort offered by only the rows of sinuous wires did not meet the needs of all. Heavier people found that the sinuous wire springs designed for people of average weight do not provide the desired resilience and have a tendency to bottom out. "Bottoming out" as used in this application, is a term of art generally referring to that condition in which the force which has been applied to the springs in a cushion exceeds the ability of the springs to resiliently resist the applied force, thus causing the springs to sag to a position in which further travel of the springs is restrained by supporting structure or by the fully extended springs. The use of stronger, stiffer springs, while providing more comfort to heavier persons, proved to be too hard and uncomfortable for lighter persons. The problem of providing proper support and resilience in cushion seating for heavier persons has also been compounded by the fact that the average person of today is bigger and heavier than the average person of 40 years ago. In addition, today's consumer is more sophisticated and demanding than in the past. Thus, the requirements for seat cushion constructions which can provide acceptable levels of support and comfort to a broader spectrum of people are more demanding today than in the past.
Further, the use of sinuous springs, which are attached to the top edge of the front and rear rails of the frame, placed heavy torsional forces on the rails requiring substantial reinforcing of the frame in order to maintain the frame in proper vertical and parallel alignment.
Attempts to overcome the aforementioned problems and to provide cushion seating with comfort and resilience have included the combination of sinuous springs and coil springs. The coil springs were placed between a flexible base support and the sinuous springs to provide more resilience to the sinuous spring. For example, U.S. Pat. No. 2,234,253 to Hopkes discloses a spring cushion construction which includes a plurality of parallel-disposed sinuous springs with coil springs disposed beneath them. The lower ends of the coil springs are supported by another row of sinuous springs extending transversely to the top row. U.S. Pat. No. 2,280,912 to Hopkes discloses a spring arrangement for bedsprings, boxsprings, etc. A plurality of parallel sinuous springs form the top surface of the cushion spring assembly. The sinuous springs are secured to tapered coil springs which are in turn secured to a lower level of sinuous springs transversely positioned with respect to the top sinuous springs. U.S. Pat. No. 4,597,566 to Scrivner discloses another form of spring cushion seating in which coil springs are placed between a plane of nonresilient wires, supported on the frame by helical edge springs, and a base bar. However, this patent does not provide the feel traditionally associated with the use of sinuous springs.
While the cushion spring structures of the prior art solved some of the problems inherent with sinuous wire-only spring structures by reducing the tendency to bottom out, the prior art structure still lacks the requisite combination of firmness and deep resilience which is desirable in cushion seating today.
Further, none of the prior art discloses a cushion seating structure which has the additional advantage of adjusting the firmness of the cushion to suit individual tastes. While some constructions, such as that disclosed in the previously disclosed '566 patent to Scrivner, provide for factory adjustability, and other constructions, such as that disclosed in U.S. Pat. No. 3,059,249 to Kamp, provide for a one-or-two position box spring adjustment, it has heretofore been unknown to provide a spring cushion seating construction in which the firmness of the cushion can be easily adjusted in degrees from "soft" to "firm" without requiring extensive factory manipulation.